Television transmitter



June 11, 1946.

Filed July 6, 1944 VIDEOAMPLIFIER LI &TR.AN$MITTER CREEK r102.

. 11o BEAM VEKI'ICAL BLANKING DEFLECTION AMPLIFIER GENERATO AMPLIFIER JNVENTOR. RAY

D. KELL.

ATTORNEY.

Patented June 11, 1946 UNITED STATES PATENT omen Ray D. Kell, Princeton,

Corporation of America, were N. 1., assignor to Radio a corporation or Dela- Application July 6, 1944, Serial No. 543,667 17 Claims. (Cl. ITS-7.2.)

This invention relates to an improvement in television transmitters, and to the method of and apparatus by means of which a television transmitter may be operatedto increase the sensitivity or efl'ectiveness of operation, particularly under adverse light conditions.

In-a conventional television system a television image pickup tube is provided which performs the function of translating an optical light image into a series of television image signals. This is accomplished by a scanning operation generally in static charge image agesis'nals. As is well known tothose skilled in the art, the scanning operation is accomplished by a bilateral deflection ofvthe cathode ray beam in order that substantially all or the individual elemental areas of the target surface may be The rapid deflection corresponds to the line deflection rate, whereas the slow deflection corresponds to the field deflection rate. Each time scans the target each vertical deflection of the cathode ray beam.

Interlaced scanning is frequently employed to reduce flicker eflects and simultaneously to give the eflect of improved detail, in which case the mediately preceding frame cycle. video signals generated by such tion are a result of static charge image The image or scanning operathe presence of an electrolight intensity of the optical image projected on the television pickup tube.' Y

Under. very adverse light conditions the electrostatic charge image will, therefore, be rather feeble with the result that the produced television image signals will have very low intensity. Under normal operation of a television there is a lower limit of light intensity at which a television image pickup tube can be operated to produce satisfactory signals, but in some instances, it is desirable to operate a television pickup tube under conditions of less illumination than this lower limit.

According to the present invention, therefore, i

a. provision has been made whereby television image signals of satisfactory intensity can be generated even though the light conditions are considerably subnormal. Since the charge image on the target surface in the television pickup tube is a function of the intensity of the amount of light projected upon the tube and in direct proportion to the length of time that intervenes beand the next tensity of the charge image may be increased by increasing the time interva. conditions when the light intensity cannot be inpreferred form of the present invention, the scanning cathode ray beam sion of such scanning is interrupted or discontinued for a predetermined number of vertical deflection cycles, thus permittin an appreciable electrostatic charge beam is again discontinued for a predetermined length of time. 1

produced at the receiver.

Naturally, it there is any excessive amount of movement in the object area. and it the interval between effective scanning cycles is too great, the movement will be reproduced as a blur and, fur- Th'erefore, under tive scanning cycles amount, then'the interval between be interrupted forvenes between successive effective scanning cycles due to leakage laterally across the surface of the target area, i. e., due to neutralization or an averaging of adjacent electrostatic charges on the target surface. The interval between effeccannot, therefore, be increased indefinitely, but many scanning cycles can actually be omitted without any appreciable loss of detail and without an excessive or objectionable amount of blur. In fact, systems have been operated in which only one out of ten verti cal scanning cycles is effective to produce television image signals, and in such operation the intensity of the produced image signals is materially increased, with the result that a much improved and clarified image is produced at the receiver over that which would be produced were each deflection cycle effective to produce image signals. In the absence of appreciable motion in the object area, the time interval between effective successive scanning cycles can be increased by increasing the lateral resistivity of the target surface upon which the electrostatic charge image is produced.

The present invention provides a system whereby the elimination or the formation of this scanning cathode ray beam is entirely automatic, and in which the time interval between efiectlve scanning cycles is automatically controlled in accordance with a function of the light intensity of the object area. Accordingly, should the light intensity of the object area increase by a small effective scanning cycles is automatically decreased by one or more vertical deflection cycles. It is therefore, one purpose of the present vention to provide an improved television trans satisfactory charge level even under adverse light conditions.

A still further purpose of the present invention resides in the provision of means whereby the length of time intervening between one cancellation of the charge image in a television image pickup tube and the next succeeding cancellation may be increased to include two or more normal field deflection cycles.

A still further purpose. of the present invention resides in the provision of means in a television transmitter whereby a scanning cathode ray beam in a television image pickup tube may one or 'more normal vertical deflection cycles to permit an increase in the charge image produced on a target surface.

Still another purpose resides in the provision of means and apparatus whereby only predetermined vertical deflection cycles or field cycles are actually effective to pro- 40. mitting system wherein the effective sensitivity v storage type.

' major portion tremely thin,

lapse of time between successive effective scanning cycles may be automatically controlled in accordance with the light intensity of the object Figure 1 shows a preferred form of the present invention; and

Figure 2 shows curves used in explaining the o eration of the system.

Referring now to the drawing, and particularly Figure 1 thereof, there is shown a television image pickup tube ill of the Orthican or low velocity Such a tube might include a light responsive surface I: upon which an optical image may be proiectedby means of a lens system shown generally at. The tube also includes a very fine mesh screen l6, adjacent which is positioned a target surface l8 which may be in the form of an extremely thin glass plate. Intermediate the flne mesh screen it and the light responsive surface I2 is an accelerating anode or ring 20 which may be in the form of a conthe inside surface of the tube envelope. This conducting surface is maintained positive with respect to the light responsive surface by means of a source of potential 22.

' When an optical image is projected upon the light responsive surface l2, photoelectrons will be emitted'from that surface in proportion to the inte'nsity'of the light at any particular elemental area. These photoelectrons are accelerated in the direction of and are brought to focus upon the extremely thin target surface -Iii by means of the accelerating ringor anode 2c, focal.condition is maintained by reason of the presence of an electromagnetic fleld produced by an electromagnetic coil as which surrounds the of the entire television image pickup tube. The field produced by the coil is parallel to the axis of symmetry of the tube, and maintains proper relative position of the photoelectrons released from the surface l2.

' The velocity at which the photoelectrons strike the surface of the target area i8 is suficient to produce secondary electrons in a ratio of the order of three to one, and these secondary elecl8 adjacent the light responsive surface 02, but in view of the fact that the target surface is exthis charge is readily transferred to the opposite side of the target area 98. The target area or extremely thin glass plate it has some conductivity although, due to its extremely reduced thickness, the resistance between the faces cf the target is many times less than the lateral resistance along the surface or the area l8. Accordingly. adiacent'electrostatic charges are not neutralized, yet they may be readily transferred from the one side of the plate iii to the other.

In the opposite end of the tube is located an electron gun structure which includes a cathode 28, a control electrode 30. 9. screen electrode 32, first anode M and second anode ll. The control electrode 30 is normally maintained negative with respect to the cathode 28, whereas the screen electrode is positive with respect to the oathand the ode.

The first and second accelerating anodes 34 and 38 have supplied thereto increasing positive potentials, and the electrostatic field produced at the adjacent ends of the first and secproper operating potentials may be applied to from v the electrodes of the electron gun structure any appropriate potential source which may, for example, be applied to terminals 40 and i2. tween these terminals 9. potentiometer or bleeder resistance may be connected in order that the relative potentials of the various electron gun structure electrodes may be properly chosen.

For deflecting the in mutually perpendicular directions, a vertical deflection coil 44 is provided as well as a horizontal deflecting coil 46. The horizontal deflecting coil or coils are energized by a cyclically varying current of suitable wave form which is obtained from an appropriate horizontal deflection generator 50. Similarly, the vertical deflecting coil or coils are energized from a suitable vertical deflection generator 48. Inasmuch as the present invention is not concerned with the particular type of deflection generator used, these elements are shown schematically, and may be of any well known type to develop the desired deflection of the scanning beam. Such deflection generators in normal operation would be electrically associated and interlocked with each other as taught by Bediord, for instance. in such a manner that a .certain desired harmonic relationship would exist between the frequency of operation of the two deflection generators. These deflection generators, in accordance with the invention as disclosed in Figure 1, operate continuously to produce cyclically varying electromagnetic fields in opposed transverse directpns within that portion of the tube immediate adjacent the location of the coils. Accordingly, when an .electron beam is generated by the electron gun structure, the beam is caused to be displaced bythe fields and vertical deflection axis of symmetry of the tube so that the scanning cathode ray beam is always directed against the direction normal to that As previously described, the target electrode II has produced thereon an electrostatic charge image which is a replica of the optical light image. This charge image the presence of the attraction force for the electrons cathode ray beam. If no charge it, then under certain beam. intensities and velocities, none of theelectrons of the beam will be absorbed by that particular portion of the target area when it is scanned, and as a result, all of the electrons of the beam will be returned through the tube and will impinge upon the surface of the generated cathode ray beam is in a positive direction, and charge image produces a slight 7 charge with the firstmultiplier electrode 32 where secondary electrons will be produced. These produced secondary electrons will then be accelerated toward the cylindrical multiplier electrode 34 where additional secondary electrons may be produced. These produced secondary electrons will then be collected by the collector electrode or grid structure 36 and will then be conducted from the tube along the conductor 52. If the scanned portion a positive charge image thereon, then a certain number of electrons of the scanning cathode ray beam will be absorbed thereby to cancel or neutralize the positive result that a lesser number of the scanning cathode ray beam through the tube with the result amount of current in the output conductor 52 will be present. Accordingly, as the the electrons of 3 electrostatic charge that is present on the electrode I8 is scanned by the cathode ray beam, the charge image is wholly or at least in part cancelled, and electrons not used for such cancellation will be returned through the tube, resulting in a current modulation of the returning cathode ray beam. This current modulated cathode ray beam will then produce variations in current in the output conductor 52, and these variations in current or potential are the television image signals.

In order to causethe television pickup tube to operate at an optimum condition it is desirable determined elemental area of the target surface in some instances to alter the potential of the fine mesh screen It by a small amount in order to alter the average number of electrons that are reach the target surface I 8. Under conditions of low light intensity, it has been found desirable to apply a slight positive potential of the order of one volt to the fine mesh screen 16; whereas under conditions of rather intense light conditions, it has been found desirable to operate the television pickup tube with a negative potential applied to the fine mesh screen l6 of the order of a volt. In order that the potential of the screen l6 may be altered within the desired limits, a potentiometer 54 is provided and a low potential difference is applied between the ends of the resistance element of the potentiometer. The mesh screen I8 is then connected by way of resistance 58 to a movable contact associated with the potentiometer.

The television image signals available from conductor 52 are then applied to appropriate amplifiers for increasing the intensity of the signals so that the image or video signals may be used to modulate a source of radio frequency energy in order that the. signals may be transmitted to remotely located receivers. The transmitted video signals generated include, in addition to the image' signals, appropriate synchronizing signals'for maintaining the desired decrease of synchronous operation between the transmitter and the receivers. Since the present invention is not concerned with the particular amplifier or transmitting system utilized. such apparatus is represented schematically as ap- .the manner of a cathode coupled denser it, while interval of tube 60 becomes conductive with the able to operate the pickup tube in such a manner that satisfactory television image signals may be produced under extremely adverse light conditions, and the intensity the produced image signals is increased by permitting an increased time interval within which the charge image present on the target electrode I8 is produced. In order to prevent a repeated cancellation or obliteration of the charge image for each vertical deflection cycle, the scanning cathode ray beam is interrupted for a predetermined number of vertical deflection cycles, and after a satisfactory charge'image has been produced, the scanning cathode ray beam is then permitted to be generated during one vertical deflection cycle following which the beam is again interrupted.

- For this purpose, a pair of tubes ti! and 82 are provided, and these tubes operate somewhat in multivibrator. Each tube includes a cathode, a control electrode,

' and an anode, and the cathodes of the two tubes are connected to a point of fixed potential by a common cathode resistance 63. The control electrode oi the tube 60 is connected to ground by way or grid resistance 66', and potential impulses of the vertical deflection frequency are applied to this control electrode by way of coupling condenser 68. It is preferable that these control impulses be of relatively short duration, and they may be derived, for example, from the vertical deflection generator 68. lhe wave forms of the voltage variations of vertical deflection frequency which are applied to the control electrode of tube 86 are represented, for example, by curve C of Figure 2. The anode of tube tit is connected to terminal ii to which a source of positive potential is applied, and the connection includes load resistance Mia The anode of tube til is coupled to the control electrode of tube 62 by coupling con. the control electrode of tube 52 is connected by way of resistance 80 to the movable arm of a single-pole double-throw switch it.

With the switch in the lower position, the switcharm IQ is connected to a point of fixed potential by Way of a variable resistance 82, the purpose of which will be described later. The anode of tube 62 may be connected directly to the terminal 12 and to the source oi positive potential,

In operation, tubes be and t2 are alternately rendered conductive, and the value of the cathode resistance as is so chosen that the conducting interval of tube 62, i. e. the non-conducting St, corresponds to one vertical deflection cycle.

to is in a non-conducting condition, and at the ion of one vertical deflection cycle, tube result that the anode of tube to changes rapidly concl' potential at the in a negative direction due to current flow through the tube anddue to the voltage drop across resistances It. This produces a negative impulse on the control electrode of tube at by way of condenser it which drives the control electrode or tube '62 considerably negative with respect to its cut oil potential as mdicatsd by the vertical portion 85 of the curve 33 shown in Figure 2. lThe cut on potential of the tube is indicated by the dotted line list associated with the curve.

This negative potential gradually changesin aposltive direction, and the rate oi such change is determined by the value of the resistance included in the control electrode circuit of tube 62. ii the resistance of potential of the 82 is made small, the change control electrode at tube 62 along he eurved portion 823 oi the curve B It will be assumed that-tube curve A of Figure electrode 36 of the electron 8 in Figure 2 will be relatively rapid; whereas, it the resistance 81 is made relatively high, this change of potential in a positive direction will be much slower. During this change of potential, negative impulses of vertical deflection ire-a quency continue to be applied to the control elec= trode of tube 60 and produce relatively short and somewhat low intensity positive impulses at the anode of tube as indicated at in the 2. These same positive impulses appear at the control electrode of tube 62 as indicated at 92 in curve B. After the potential or the control electrode or tube or has gradually changed in a positive direction and approaches the cut'ofl potential of tube 82, one of these positive impulses will render tube 62 conductive with the result that the increased current through the common cathode resistance 6Q places a negative bias on tube Bil, resulting in a non-conducting condition of tube 60, which enhances the positive potential applied to tube 62 as indicated bv the short vertical portion 26 of the curve B shown in Figure 2 During the time that tube 69 is in a non-conducting condition, a positive potential or impulse, indicated at 36 in curve A, is produced at the anode of tube Gil, and the duration ofthis impulse is regulated to correspond to the duration of one vertical defiection cycle. Accordingly, there will be present at the anode of tube 60 a series of positive impulses 963 (see curve A of Figure 2), the time duration of each of the impulses corresponding to one vertical deflection cycle, The time inter= val between impulses depends upon the amount of resistance included in the control electrode circuit of tube 62. These positive impulses, cor responding to one vertical deflection cycle, are then'applied, by way of conductor 98, to a beam blanking amplifier Hill where their intensity is increased. After the desired degree of amplincation, the impulses are then applied to the control electrode 8! of the electron gun structure by way of conductor 682. r

The voltage variations applied to the control gun structure, therefore, have a wave form similar to the wave form of curve A of Figure 2 and. this voltage varia= tion results in the formation or a cathode ray beam only during the intervals of the positive impulses, represented at 96. During the time beam is generated. As stated above, the parameters of the circuit. and particularly the oath ode resistance 6d, are so chosen that the duration of the positive impulses corresponds to one vertical deflection cycle while the interval between impulses corresponds to one or more whole vertical deflection cycles, the number depending upon the amount of resistance included in the grid circuit of the tubetii. It is thereiore possible to permit the production of a cathode ray beam for the duration of one vertical deflection cycle and'to preclude the production oi such a beam for the next succeeding several vertical defiection cycles. The positive charge image pro duced on the target surface it is permitted to accumulate to an appreciable value during field cycleswhen no cathode ray bears is gen erated. During the vertical olefiectimzlv e that ing an appreciable intensity, and the scanning "seam cancels or neutralizes all, or an apprcci able portion, oi the charge image produc 'i the lt these impulses, no cathode ray the inactive be unilateral, the tubes MB optical image is extremely low, then the value oi! resistance 82 may be increasedto increase the appreciable inof ineffective cycles controlled manually by means optical image is below that which would normally be required for the production of a satis-' factory image signal series. The value of the resistance 82 may be conveniently manually controlled in accordance with existing light conditions.

There are instanceswhen it is desirable to alter period automatically in accordance with variations with light intensity, and for this purpose a means is provided which is responsive to the light intensity of the object area. This means includes a light responsive cell I I0 such as, for example, a photoelectric tube upon which light from the object area is projected by'means of an optical system shown generally at H2. The current generated by the light responsive cell is supplied to a direct current amplifier I which may be of any appropriate design in order that the intensity of the currents generated by the light responsive cell may be appropriately increased. Two electron discharge tubes H6 and H8 are provided, each of which includes a oathode, a control electrode, and an anode. The control electrodes of these tubes are connected in parallel and are supplied with potentials from the direct current amplifier Ill'in order that the length of the interval between eilective scanning cycles in accordance with the variations in the light intensity of the object area. Under conditions when the light intensity of the object area may vary during operation of the television pickup tube, such automatic control is desirable and the selector switch will be placed in the upper position as indicated in the drawing. If, however, lighting conditions remain substantially uniform or fixed, then the selector be placed in the lower position, and the number of potentiometer 82.

From the above description it will therefore be apparent that a television pickup tube may be operated under extremely adverse light conditions yet the mode of operation may be so arranged that image signals of acceptable intensity may be produced by the pickup tube by the expedient of rendering the pickup tube ineffective for one or Following the inactive period, the television pickup tube is rendered active or effective to produce television corresponding to one vertical deflection cycle following which the tube is again rendered ineflective for a period of time inversely proportional to the light intensity of the object area.

Although the present invention isdescribed somewhat in detail and although a more or less specific type of television pickup tube is shown and described herein, it is to be understood that various other television image pickup tubes could as well be employed so long as thetube involves an electron storage method of operation.

'Various other alterations and modifications may be made in the present invention without departing from the spirit and scope thereof, and

potentials of the control electrodes may be varied with respect to their associated cathodes. The cathode of one tube, for example tube I it, and

the anode of tube i l8 are connected together and switch "is in the sistance or internal impedance of tubes H6 and H8. In order that this resistance path will'not and H8 are reversely connected as indicated in the drawing. The application of a varying potential to the control electrodes-or these tubes results in an alteration in the internal impedance of the tubes with the result that their eiiectiveresistance may be increased or decreased in accordance with the applied potentials. Since the applied potentials are derived from the direct current amplifier H4, which is energized from the light responsive tube till, the extent of the potentials applied to the tubes I I6 andi i9 is a function of the light intena sity of the object area. The polarity of the potentials derived from the direct current amplifier isso arranged that upon an increase in the light intensity of the object area, the eflective impedance of the tubes H6 and I I8 is decreased; whereas if the light intensity of the object area decreases, the effective impedance of the tubes H6 and H8 increases. By it is therefore possible to automatically alter 'the means of such a control it is desired that any 'and all such modifications be considered within the purview of the present invention except as limited by the hereinafter appended claims.

Having described my invention, what I claim is:

1. A method of developing television signals which comprises forming electrostatic charges to represent the light values of a. subject to be televised, electronically converting the produced charges into video signals at a pro-established conversion rate and controlling the lugs between successive charge to signal conversions in accordance with the average brightness value of the subject beingtelevised.

2. The method of operating a. television pickup tube which comprises the steps of producing an electrostatic charge image or an object to be televised, generating a cathode ray beam, utilizing' the generated cathode ray beam to convert the electrostatic charge image into electrical signals, and inerrupting the generation of the math ode ray beam for predetermined time intervals each at least equivalent to the image to signal conversion intervals to permit the formation 01' an enhanced electrostatic charge image.

3. The method of operating a televisionpickup tube wherein an electrostatic charge image is formed from an optical light image which comprises the steps of generating a cathode ray beam,

cyclically scanning the electrostatic charge image by the generated cathode ray beam to produce television image siganls, and successively interrupting the generated whereby a more intense electrostatic charge image may be formed.

4. The method of operating a television pickup switch 18 may 7 more vertical deflection cycles.

image signals for, an interval cathode ray beam fora predetermined whole nuznber of scanning cycles televised, generating a cathode ray beam,

tube wherein an electrostatic charge image is formed from an optical light image which comprises the steps of generating a cathode ray beam,

cyclically scanning the'electrostatic charge image by the generated cathode ray beam to produce a series of television image signals, and successively interrupting the scanning operation fora predetermined whole number of scanning, cycles whereby an enhanced electrostatic charge image may be formed between eflective scanning cycles.

5. The method of operating a television pickup tube which comprises the steps producing an electrostatic charge image of an object to' be deflectcathode ray beam in a predeto convert the electrostatic electrical signals, interrupting the cathode ray beam for predetermined time intervals to permit the formation of an enhanced electrostatic charge image, and controlling the beam interruption time intervals in accordance with the light intensity oi the object to be televised.

6. The method of operating a television pickup tube wherein an electrostatic charge image is formed from an optical light image which comprises the steps ot generating a cathode ray beam, cyclically scanning the electrostatic charge image by the generated cathode ray beam to produce television image signals, successively interrupting the generated cathode ray beam for a predetermined whole number of scanning cycles to permit the formation of a more intense electrostatic charge image, and altering terval in accolidance with the light intensity of the optical image.

'7. A television ing the generated termined pattern charge image into the generation of transmitter including a televl sion pickup tube having a target electrode, means electrostatic charge image on for producing an the target electrode corresponding to an optical light image, an electrode gun structure including the interruption in-' an optical light image, an electrode gun structure including an intensity control electrode for generating a cathode ray beam, beam deflecting means for causing the generated cathode ray beam to cyclically scan the target electrode for each television field to produce and means for modulating the potential of the control electrode to interrupt the cathode ray beam tor a time interval corresponding to a predetermined whole number oi field scanning cycles to permit the formation of an intensified electrostatic charge image on the target electrode prior to the next succeeding scanning cycle.

10. A television transmitter including a television pickup tube having a target electrode upon which an electrostatic charge image of an object area is adapted to be produced, means for cycli cally scanning the target electrode by a cathode an intensity control electrode'ior generating a cathode ray beam, beam deflecting means for causing the generated cathode ray beam to perform successive field scanning'cycles oi the target electrode to produce television image signals, and means for producing a voltage variation of rectangular wave form for modulating the potential oi the control electrode to intermittently interrupt the cathode ray beam for time intervals corresponding to a predetermined whole number of field scanning cycles to permit the production of an intensified electrostatic charge image on the target electrode prior to each efiective scanning cyc e. r

8. A television transmitter including a television pickup tube having a target electrode, means ror producing an electrostatic charge image on the target electrode corresponding to an optical a predetermined number of frame scanning cycles to permit the formation of an enhanced eleotrostatic charge image on the target electrode prior to the next effective scanning cycle.

beam deflecting 9. A television transmitter including a tele= vision pickup tube having a target electrode,

means for producing an electrostatic charge image on the target electrode corresponding to so complete ray beam to convert the electrostatic charge image into a series of television image signals representing television fields, and means for repeatedly precluding the scanning oi the target electrode for a, predetermined number of whole field scanning cycles whereby; the electrostatic charge image that is produced on the target electrode will be increased in intensity.

11. A televisiontransmitter including a television pickup tube having a target electrode upon which an electrostatic charge image of an optical light image is adapted. to be produced, means ior cyclically scanning the target electrode by a oath= ode ray beam to convert the electrostatic charge image into a series of television image signals representing successive television fields, means for repeatedly precluding the scanning oi the tar get electrode for a predetermined number of whole field scanning cycles following each efiective field scanning cycle whereby the electrostatic charge image that is produced on the target electrode will be increased in intensity, and means for altering the intervals during which the scam ning operation is precluded by one or more whole field scanning cycles.

12. A television transmitter including a tele vision pickup tube having a target electrode upon which an electrostatic charge image of an object area is adapted to be produced, means for cyclically scanning the target electrode by a cathode ray beam to convert image into a series 0! television image signals, means for intermittently interrupting the scanning of the target electrode, each interruption interval corresponding to a predetermined num= ber of whole scanning cycles whereby the elect-r0 static charge imagethat is produced on the tar get electrode will be increased in intensity be-- tween efiective scanning cycles, and means responsive to the light intensity oi the object area for altering the duration of the interruption intervals. I

13. A. television transmitter including a tale vision pickup tube having a target electrode upon which is produced an electrostatic charge image oi an optical light image, an electron gun struc-= ture for generating ,a scanning cathode ray beam, means ior deflecting a generated cathode ray beam in predetermined directions inorder to pro duce successive television frame scanning cycles to scan the target electrode to convert the, clos trostatic charge image into television image sig nals and means to permit the generation at a cathode ray beam during certain frame cycles, the interval between cathode ray seam generation intervals corresponding to one or. ore irame scanning cycles and the dam television image signals,

the electrostatic charge tion of each cathode ray beam generation interture for generating a scanning cathode ray beam,

means for deflecting a generated cathode ray beam in substantially mutually perpendicular directions in order to scan the target area to convert the electrostatic charge image into television image signals corresponding to a television field, means to permit the formation of a cathode ray beam during certain field scanning cycles, the

' time interval between formations of the cathode ray beam corresponding to one or more complete field scanning cycles and the duration of the formation of the cathode ray beam corresponding to at least one field scanning cycle, and means for altering the time interval between successive formations of the cathode ray beam, whereby the intensity of the electrostatic charge image present on the target area at the time the target area 'is scanned by the formed cathode ray beam may' be increased in intensit h 15. A television transmitter including a television pickup tube having. a target electrode upon which is produced an electrostatic charge image of an optical light image, an electron gun structure for producing a scanning cathode ray beam, means for cyclically deflecting a produced cathode ray beam in substantially mutually perpendicular directions in order to scan the target electrode to convert the electrostatic charge image into television image signals, means to repeatedly prevent the production of a cathode ray beam during .certain scanning cycles, the intervals that production of the cathode ray beam, is prevented corresponding to one or more complete scanning cycles and the duration-of cathode ray beam corresponding to at least one scanning cycle, and means for altering the interval between successive productions of the cathode ray beam by one or more complete scanning cycles, whereby the intensity of the electrostatic charge image present on the target electrode may be enhanced between the production intervals.

16. A television transmitter including a television pickup tube having a target electrode, means for producing an electrostatic charge image on the target electrode corresponding to an optical light image of an object area to be televised, an electron gun structure including a beam intensity control electrode for generating a cathode ray beam, beam deflecting means for causing the generated cathode ray beam to cyclically scan the target electrode to convert the electrostatic charge image into television image signals corresponding to successive television fields, means for intermittently preventing the generation of the cathode ray beam for a predeermined number of field scanning cycles and for intermittently permitting the generation of the cathode ray beam for a time interval corresponding to one field scanning cycle whereby the intensity of the electrostatic charge image may be increased between each effective scanning cycle, and means for altering, by one or more field scanning cycles, the time interval during whichthe generation of the cathode ray beam is prevented in accordance with the light intensity of the object area to be televised.

17. A television transmitter including a television pickup tube having a target electrode, means for producing an electrostatic charge image on the target electrode corresponding to an optical light image of an object area. to be televised, an electron gun structure including a beam intensity control electrode for generating a cathode ray beam, beam deflecting means for causing the generated cathode ray beam to cyclically scan the target electrode to convert the electrostatic charge image into television image signals, means for producing a voltage variation of substantially rectangular Wave form, means to apply theprcduced voltage variation to the intensity control electrode to intermittently prevent and permit the generation of a cathode ray beam in synchronism and in phase with the scanning ,opera'tion whereby the intensity of the electrothe producing of the v static charge image may be effective scanning cycles, and

increased between ject area to be televised, the time interval during which the generation of the cathode ray beam means for altering in accordance with the light intensity of the ob-' 

